1. Field of the Invention
The present invention is in the field of pollution control and specifically relates to a reusable cartridge for use in a storm drain to prevent liquid hydrocarbons from being carried by runoff water into sensitive waterways.
2. The Prior Art
In U.S. Pat. No. 3,382,170 Pape discloses a method of removing an oil film from a body of water by using expanded perlite that has been coated with a silicone for preferentially absorbing the oil and rejecting the water. Perlite is a generic term for a naturally occurring siliceous volcanic rock. Variations of Pape's disclosure are found in U.S. Pat. No. 3,674,683 to Ranier; U.S. Pat. No. 3,770,575 to Ball; U.S. Pat. No. 4,142,969 to Funk et al.; and, U.S. Pat. No. 5,302,590 to Newman.
Of course one cannot simply fill the storm drain with treated perlite; that would greatly reduce the capacity of the storm drain to handle heavy runoff. Also, after it has absorbed several times its own weight in hydrocarbons, the perlite becomes spent and needs to be replaced.
To avoid interfering with the flow of large amounts of water through the storm drain, a pending U.S. patent application of a different inventor discloses the use of an insert that fits into the mouth of a storm drain and that confines the perlite to a space immediately adjacent the vertical walls of the storm drain. In this arrangement, at low runoff rates the water will trickle through the perlite filter, but at greater runoff rates the water will simply cascade over the filter, bypassing it.
Although in theory the perlite could be disposed loosely in the insert, that approach is not practical for several reasons. Turbulence of the water would flush the perlite away unless the perlite were contained. However, if the perlite is contained loosely in the insert, removal of the spent perlite and its replacement by fresh perlite would become a problem. Further, the flow pattern of the incoming stream might be heavier in one region than in another, and this could cause displacement of the loose perlite and/or the production of rat holes to such an extent that the filtering action would be impaired.
The present inventor has solved all of these problems by providing a cartridge to confine the perlite within the insert, which cartridge is replaceable, refillable, and reusable.